A few things.....
Why Crtis over Stands? I can see why Spark Kid Dragoon can be good but why not Lizard Soldier, Saishin and Raien blocks Intercepts right?

Saishin is pathetic because:
1) It only targets G0 units
2) It requires the boosted unit to actually HIT the VG, which means that your opponent can simply guard against the attack if they want to protect their G0 for whatever reason
3) Frankly, there are very few clans that have G0 rearguards, and off the top of my head the only ones that you would want to retire ASAP are Conroe and Crimson Lion. In short, not enough targets to make it worth while.
4) Because of the above reasons, you probably won't be able to use his skill much, which means you'll be stuck with a 5k rearguard. At least Spark Kid can be used whenever you wanted to.

Raien stops intercepts yes, he's basically there for the big push for Final Turn. Plus, he's a 7k booster, so he's decent.
As for Crits over stands..... personal preference. You could easily keep the stands and swap out the Carbuncles for the Djinns if you wish.

Dudes...Narukami basically is a copy of Kagero. So they share the same strategy: kill your opponents rg line-up.
As for now I see only two types of builds:
First, based on consistency
Second, based on full lockdown.
G0
1xSpark Kid Dragoon
4xDjin of the Poison Mind
4xYellow Gem Carbuncle
4xOld Dragon Mage

I don't think Saishin is bad at all, personally. It's a little bit of anti-meta in a deck that otherwise has none. Granted, you have to go first for it to really be useful, but I'd take whatever I can get to snipe Barcgal, Conroe, and Kyrph. The things are monsters. Spark-Kid does have his merits though.

At the moment I believe Narukami's best bet is more or less: Ride Vermillion, limit break, follow up with 1 or 2 Gunners on the next turn, swing for game since your opponent's defensive resources are extremely limited.

For something a little cheaper, it's possible to build around Indra too.

Thas fair, I like him better then Vortex Dragon. I play tested him yesterday, and I was losing badly I had played him as Vandguard a turn or to before
Two turns after I was brought to 5 dmg vs. 2, then on my turn I used Gairas first effect and then used Spark Kid. Then I called 2 Desert Gunner Raien to RG and used Gairas effect then went swinging.

Depends. Both Spark Kid and Saishin have their good points and bad points.

Saishin can potentially devastate your opponents moving starter plays or act as a damage deterrent early in the game. Sniping your opponent's starter could seriously slow them down. But there might be times when you can't use his ability because your opponent doesn't have a grade 0 to hit (though it isn't a total loss, because you still have a unit that can boost on the field until you don't need it).

Spark Kid can potentially get you the grade 3 that you need, but there's a good chance that it can whiff and there not be a grade 3 in your next 5 cards (meaning you wasted a counterblast AND lost a unit for nothing).

It all comes down to player preference. If you find yourself having a problem getting grade 3s in your hand or you never miss Spark Kid's effect, then go with Spark Kid. If you want a chance at disrupting your opponents opening plays, than go with Saishin.